GUARD DUTY
When I was in the U.S. Army, I remember we had to pull guard duty many times. The purpose of guard duty was to ensure that other soldiers, equipment, or areas were protected from the enemy. I can recall that in basic training, or boot camp, we had to memorize three General Orders and the first one was, "I will guard everything within the limits of my post and quit my post only when properly relieved."
When we were properly relieved, there was a password that was spoken between the person on guard duty and the one that was relieving them. If the improper password was given, you were not properly relieved. The safety of all that was being guarded depended upon you, the person on guard duty. If something went wrong or the enemy was able to get access into that which you were responsible for guarding, then you were held accountable and punishment was inevitable.
(From a sermon by Melvin Maughmer, Jr., Guard Duty, 5/25/2011)